oxyplot: BUG : PngExporter generates empty images

PngExporter produces an empty output If the user that started the application is not currently logged in.

Steps to reproduce

1. Log into a remote PC
2. Start the application that periodically saves a png file using

var pngExporter = new PngExporter { Width = 2000, Height = 1000, Background = OxyColors.White };
            pngExporter.ExportToFile(pm, filepath);

1. logout from the remote pc
2. Check that the images stored when the remote connection is active are correctly saved and the one without an active remote connection are blank.

Platform: .NET version: 4.5 (windows form) Version oxyplot 2.0

Expected behaviour

The export file should be correctly exported regardless of the remote connection state.

Actual behaviour

If a remote connection is active or the user directly log in into the machine all works fine. If the user that started the application is not currently logged in all exported images are blank.